U.S. patent application number 11/153813 was filed with the patent office on 2006-01-12 for feed forward amplifier with multiple cancellation loops capable of reducing intermodulation distortion and receive band noise.
Invention is credited to Khosro Shamsaifar.
Application Number | 20060009172 11/153813 |
Document ID | / |
Family ID | 35839696 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060009172 |
Kind Code |
A1 |
Shamsaifar; Khosro |
January 12, 2006 |
Feed forward amplifier with multiple cancellation loops capable of
reducing intermodulation distortion and receive band noise
Abstract
An embodiment of the present invention provides an apparatus,
comprising a feed forward amplifier capable of receiving an input
signal and including a plurality of cancellation loops, wherein at
least one of the cancellation loops includes a tunable delay line
enabling the reduction of intermodulation distortion and receive
band noise when outputs from the plurality of cancellation loops
are combined with the input signal to the feed forward amplifier.
In an embodiment of the present invention the plurality of
cancellation loops may be two cancellations loops and a tunable
delay line may be included in both of the cancellation loops.
Further, the tunable delay line may be a voltage tunable delay line
that includes a voltage tunable dielectric capacitor to facilitate
the control of the tunable delay and the voltage tunable dielectric
capacitor may include a layer of voltage tunable dielectric
material positioned on a surface of a low loss, low dielectric
substrate.
Inventors: |
Shamsaifar; Khosro;
(Ellicott City, MD) |
Correspondence
Address: |
James S. Finn;C/O William Tucker
14431 Goliad Dr.
Box #8
Malakoff
TX
75148
US
|
Family ID: |
35839696 |
Appl. No.: |
11/153813 |
Filed: |
June 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60586437 |
Jul 8, 2004 |
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Current U.S.
Class: |
455/114.2 ;
375/296 |
Current CPC
Class: |
H03F 1/3223 20130101;
H03F 1/3229 20130101; H04B 1/126 20130101 |
Class at
Publication: |
455/114.2 ;
375/296 |
International
Class: |
H04B 1/04 20060101
H04B001/04; H04K 1/02 20060101 H04K001/02; H04L 25/03 20060101
H04L025/03 |
Claims
1. An apparatus, comprising: a feed forward amplifier capable of
receiving an input signal; and a plurality of cancellation loops
associated with said feed forward amplifier, wherein at least one
of said plurality of cancellation loops includes a tunable delay
line enabling the reduction of intermodulation distortion and
receive band noise when outputs from said plurality of cancellation
loops are combined with said input signal to said feed forward
amplifier.
2. The apparatus of claim 1, wherein said plurality of cancellation
loops are two cancellations loops and a tunable delay line is
included in both of said cancellation loops.
3. The apparatus of claim 1, wherein said tunable delay line is a
voltage tunable delay line.
4. The apparatus line of claim 3, wherein said tunable delay line
includes a voltage tunable dielectric capacitor to facilitate the
control of said tunable delay.
5. The apparatus of claim 4, wherein said voltage tunable
dielectric capacitor includes a layer of voltage tunable dielectric
material positioned on a surface of a low loss, low dielectric
substrate.
6. The apparatus of claim 5, wherein said voltage tunable
dielectric capacitor further includes a pair of electrodes
positioned on said layer of voltage tunable dielectric material and
separated by a gap, with an input line connected with a first
electrode of said pair of electrodes and an output line connected
with a second electrode of said pair of electrodes.
7. The apparatus of claim 6, wherein said voltage tunable
dielectric capacitor further includes a variable DC voltage source
connected between said pair of electrodes to supply a control
voltage to said voltage tunable dielectric capacitor.
8. The apparatus of claim 2, further comprising an input signal,
said input signal including a receive band noise component and an
intermodulation interference component and wherein the enabling of
the reduction of intermodulation distortion and receive band noise
when said plurality of cancellation loops are combined is
accomplished by said tunable delay line of said first cancellation
loop delaying the noise component by 180 degrees of said input
signal and said delay line of said second cancellation loop
delaying the intermodulation interference component by 180 degrees
such that when the input signal and said signals from said first
and said second cancellation loops are combined, the noise signal
component and the intermodulation signal component are cancelled
from said input signal.
9. A method of reducing intermodulation distortion and receive band
noise in a signal that is input into a feed forward amplifier,
comprising: applying a first cancellation loop to said input
signal, said first cancellation loop including a tunable delay line
capable of delaying a noise component to said input signal;
applying a second cancellation loop to said input signal, said
second cancellation loop including a tunable delay line capable of
delaying an intermodulation noise component to said input signal;
and combining said input signal and the output of said first
cancellation loop and the output of said second cancellation loop
to produce an output signal with reduced noise and intermodulation
interference.
10. The method of claim, wherein said tunable delay line is a
voltage tunable delay line.
11. The method line of claim 10, wherein said tunable delay line
includes a voltage tunable dielectric capacitor to facilitate the
control of said tunable delay.
12. The method of claim 11, wherein said voltage tunable dielectric
capacitor includes a layer of voltage tunable dielectric material
positioned on a surface of a low loss, low dielectric
substrate.
13. The method of claim 12, wherein said voltage tunable dielectric
capacitor further includes a pair of electrodes positioned on said
layer of voltage tunable dielectric material and separated by a
gap, with an input line connected with a first electrode of said
pair of electrodes and an output line connected with a second
electrode of said pair of electrodes.
14. The method of claim 12, wherein said voltage tunable dielectric
capacitor further includes a variable DC voltage source connected
between said pair of electrodes to supply a control voltage to said
voltage tunable dielectric capacitor.
15. The method of claim 9, further comprising passing said signal
through a passband filter prior to entering said tunable delay in
said second cancellation loop.
16. A system, comprising: a feed forward amplifier with an input
signal and an output signal; and a plurality of cancellation loops
integral to said feed forward amplifier, wherein each of said
plurality of cancellation loops contains a tunable delay line
capable of adjusting the time delay and phase of said input signal
and recombining with said input signal such that any interference
included in said input signal or generated by said feed forward
amplifier is removed prior to said output signal.
17. The system of claim 16, wherein said interference included in
said input signal or generated by said feed forward amplifier is
receiver noise or intermodulation interference.
18. The system of claim 16, wherein said plurality of cancellation
loops are two cancellations loops and a tunable delay line is
included in both of said cancellation loops.
19. The system of claim 18, wherein said tunable delay line is a
voltage tunable delay line.
20. The system of claim 19, wherein said tunable delay line
includes a voltage tunable dielectric capacitor to facilitate the
control of said tunable delay.
21. The system of claim 20, wherein said voltage tunable dielectric
capacitor includes a layer of voltage tunable dielectric material
positioned on a surface of a low loss, low dielectric substrate.
Description
CROSS REFERENCED TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending
patent application with attorney docket number
JSF01-0088/WJT08-0093 entitled, "METHOD AND APPARATUS CAPABLE OF
INTERFERENCE CANCELLATION" filed, Jun. 14, 2006 and claims the
benefit of U.S. Provisional Patent Application Ser. No. 60/586,437
filed Jul. 08, 2004.
BACKGROUND OF THE INVENTION
[0002] Electrically tunable filters have many uses in microwave and
radio frequency systems. Compared to mechanically and magnetically
tunable filters, electronically tunable filters have the important
advantage of fast tuning capability over wide band application.
Because of this advantage, they can be used in the applications
such as, by way of example and not by way of limitation, LMDS
(local multipoint distribution service), PCS (personal
communication system), frequency hopping, satellite communication,
and radar systems.
[0003] Filters for use in radio link communications systems have
been required to provide better performance with smaller size and
lower cost. Significant efforts have been made to develop new types
of resonators, new coupling structures and new configurations for
the filters. In some applications where the same radio is used to
provide different capacities in terms of Mbits/sec, the
intermediate frequency (IF) filter's bandwidth has to change
accordingly. In other words, to optimize the performance of radio
link for low capacity radios, a narrow band IF filter is used while
for higher capacities wider band IF filters are needed. This
requires using different radios for different capacities, because
they have to use different IF filters. However, if the bandwidth of
the IF filter could be varied electronically, the same
configuration of radio could be used for different capacities which
will help to simplify the architecture of the radio significantly,
as well as reduce cost.
[0004] Traditional electronically tunable filters use semiconductor
diode varactors to change the coupling factor between resonators.
Since a diode varactor is basically a semiconductor diode, diode
varactor-tuned filters can be used in various devices such as
monolithic microwave integrated circuits (MMIC), microwave
integrated circuits or other devices. The performance of varactors
is defined by the capacitance ratio, C.sub.max/C.sub.min, frequency
range, and figure of merit, or Q factor at the specified frequency
range. The Q factors for semiconductor varactors for frequencies up
to 2 GHz are usually very good. However, at frequencies above 2
GHz, the Q factors of these varactors degrade rapidly.
[0005] Since the Q factor of semiconductor diode varactors is low
at high frequencies (for example, <20 at 20 GHz), the insertion
loss of diode varactor-tuned filters is very high, especially at
high frequencies (>5 GHz). Another problem associated with diode
varactor-tuned filters is their low power handling capability.
Further, since diode varactors are nonlinear devices, their
handling of signals may generate harmonics and subharmonics.
[0006] Commonly owned U.S. patent application Ser. No. 09/419,219,
filed Oct. 15, 1999, and titled "Voltage Tunable Varactors And
Tunable Devices Including Such Varactors", discloses voltage
tunable dielectric varactors that operate at room temperature and
various devices that include such varactors, and is hereby
incorporated by reference. Compared with the traditional
semiconductor diode varactors, dielectric varactors have the merits
of lower loss, higher power-handling, higher IP3, and faster tuning
speed.
[0007] High power amplifiers are also an important part of any
radio link. They are required to output maximum possible power with
minimum distortion. One way to achieve this is to use feed forward
amplifier technology. A typical feed forward amplifier includes two
amplifiers (the main and error amplifiers), directional couplers,
delay lines, gain and phase adjustment devices, and loop control
networks. The main amplifier generates a high power output signal
with some distortion while the error amplifier produces a low power
distortion-cancellation signal.
[0008] In a typical feed forward amplifier, a radio frequency (RF)
signal is input into a power splitter. One part of the RF signal
goes to the main amplifier via a gain and phase adjustment device.
The output of the main amplifier is a higher level, distorted
carrier signal. A portion of this amplified and distorted carrier
signal is extracted using a directional coupler, and after going
through an attenuator, reaches a carrier cancellation device at a
level comparable to the other part of the signal that reaches
carrier cancellation device after passing through a delay line. The
delay line is used to match the timing of both paths before the
carrier cancellation device. The output of carrier cancellation
device is a low level error or distortion signal. This signal,
after passing through another gain and phase adjustment device,
gets amplified by the low power amplifier. This signal is then
subtracted from the main distorted signal with an appropriate delay
to give the desired non-distorted output carrier.
[0009] Traditionally, delay lines have been used to give the
desired delay and provide the above-described functionality.
However, delay filters have become increasingly popular for this
application because they are smaller, easily integrated with other
components, and have lower insertion loss, as compared to their
delay line counterpart. A fixed delay filter can be set to give the
best performance over the useable bandwidth. This makes the
operation of a feed forward amplifier much easier, as compared to
the tuning of a delay line, which simulates adjustment of the
physical length of a cable. However, fixed delay filters still have
to be tuned manually.
[0010] There is a need for high performance, small size tunable
bandwidth filters for wireless communications applications, as well
as other applications. There is a further need for a method and
apparatus capable of interference cancellation.
SUMMARY OF THE INVENTION
[0011] An embodiment of the present invention provides an
apparatus, comprising a feed forward amplifier capable of receiving
an input signal and including a plurality of cancellation loops,
wherein at least one of the cancellation loops includes a tunable
delay line enabling the reduction of intermodulation distortion and
receive band noise when outputs from the plurality of cancellation
loops are combined with the input signal to the feed forward
amplifier. In an embodiment of the present invention the plurality
of cancellation loops may be two cancellations loops and a tunable
delay line may be included in both of the cancellation loops.
Further, the tunable delay line may be a voltage tunable delay line
that includes a voltage tunable dielectric capacitor to facilitate
the control of the tunable delay and the voltage tunable dielectric
capacitor may include a layer of voltage tunable dielectric
material positioned on a surface of a low loss, low dielectric
substrate. The voltage tunable dielectric capacitor may further
include a pair of electrodes positioned on the layer of voltage
tunable dielectric material and separated by a gap, with an input
line connected with a first electrode of the pair of electrodes and
an output line connected with a second electrode of the pair of
electrodes. Further, the voltage tunable dielectric capacitor may
include a variable DC voltage source connected between the pair of
electrodes to supply a control voltage to the voltage tunable
dielectric capacitor.
[0012] In an embodiment of the present invention, the present
invention may further comprise an input signal, the input signal
including a receive band noise component and an intermodulation
interference component and wherein the enabling of the reduction of
intermodulation distortion and receive band noise when the
plurality of cancellation loops are combined is accomplished by the
tunable delay line of the first cancellation loop delaying the
noise component by 180 degrees of the input signal and the delay
line of the second cancellation loop delaying the intermodulation
interference component by 180 degrees such that when the input
signal and the signals from the first and the second cancellation
loops are combined, the noise signal component and the
intermodulation signal component are cancelled from the input
signal.
[0013] An embodiment of the present invention also provides a
method of reducing intermodulation distortion and receive band
noise in a signal that is input into a feed forward amplifier,
comprising applying a first cancellation loop to the input signal,
the first cancellation loop including a tunable delay line capable
of delaying a noise component to the input signal, applying a
second cancellation loop to the input signal, the second
cancellation loop including a tunable delay line capable of
delaying an intermodulation noise component to the input signal,
and combining the input signal and the output of the first
cancellation loop and the output of the second cancellation loop to
produce an output signal with reduced noise and intermodulation
interference.
[0014] Yet another embodiment of the present invention provides a
system, comprising a feed forward amplifier with an input signal
and an output signal and a plurality of cancellation loops integral
to the feed forward amplifier, wherein each of the plurality of
cancellation loops contains a tunable delay line capable of
adjusting the phase of the input signal and recombining with the
input signal such that any interference included in the input
signal or generated by the feed forward amplifier is removed prior
to the output signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention is described with reference to the
accompanying drawings. In the drawings, like reference numbers
indicate identical or functionally similar elements. Additionally,
the left-most digit(s) of a reference number identifies the drawing
in which the reference number first appears.
[0016] FIG. 1 is a schematic representation of a lumped element
tunable bandwidth band-pass filter constructed in accordance with
this invention.
[0017] FIG. 2 is a schematic representation of an edged coupled
microstrip line band-pass filter with tunable varactors.
[0018] FIG. 3 is a top plan view of a varactor that can be used in
the filters of this invention.
[0019] FIG. 4 is a cross-sectional view of the varactor of FIG. 3,
taken along section 4-4 of FIG. 3.
[0020] FIG. 5 is a schematic representation of feed forward
amplifier that uses a tunable delay filter in accordance with this
invention.
[0021] FIG. 6 is a flow diagram illustrating the method of the
present invention.
[0022] FIG. 7 illustrates a signal spectrum at the input which
includes a transmit signal and receive noise of one embodiment of
the present invention.
[0023] FIG. 8 illustrates a signal spectrum at point "a" of FIG. 12
including a transmit signal and receive noise and intermodulation
signals one embodiment of the present invention.
[0024] FIG. 9 illustrates the signal spectrum at point "b" of FIG.
12 and intermodulation signals of one embodiment of the present
invention.
[0025] FIG. 10 illustrates the Signal spectrum at point "c" of FIG.
12 with Transmit signal and Receive noise amplified of one
embodiment of the present invention.
[0026] FIG. 11 illustrates the signal spectrum at point "d" of FIG.
12 with receive noise of one embodiment of the present
invention.
[0027] FIG. 12 illustrates a feed forward power amplifier capable
of reducing intermodulation distortion and receive noise of one
embodiment of the present invention.
DETAILED DESCRIPTION
[0028] Referring to the drawings, FIG. 1 is a schematic
representation of a lumped element tunable bandwidth band-pass
filter 10 constructed in accordance with this invention. Filter 10
includes an input 12, an output 13 and a plurality of resonators
14, 16, 18. A first voltage tunable dielectric access varactor 20
couples input 12 with resonator 14. A second voltage tunable access
dielectric varactor 22 couples output 13 with resonator 18.
Additional intercavity varactors 24, 26 are connected between
adjacent resonators 14, 16, 18. Each of voltage tunable access
varactors 20, 22 and each of voltage tunable intercavity or
varactors 24, 26 includes a voltage tunable dielectric material
having a dielectric constant that varies with an applied control
voltage, also called a bias voltage. By changing the control
voltage for a respective varactor 20, 22, 24, 26, the capacitance
of the respective varactor 20, 22, 24, 26 changes.
[0029] In tunable bandwidth bandpass filter 10 (FIG. 1), the
coupling between adjacent resonators 14, 16, 18 is achieved by a
variable intercavity capacitor or varactor 24, 26. By changing the
bias voltage of a respective intercavity varactor 24, 26 its
capacitance value will change which provides a change in coupling
factor. Similarly, access coupling of input 12 through access
varactor 20 or access coupling of output 13 through access varactor
22 can be controlled by tuning appropriate access varactors 20, 22.
Bandwidth of filter 10 is defined by intercavity coupling (i.e.,
coupling among resonators 14, 16, 18), as well as access coupling
through access varactors 20, 22 Therefore, by tuning these various
couplings the bandwidth of filter 10 can be tuned or changed.
[0030] When varactors 20, 22, 24, 26 are biased, their capacitance
values are smaller, resulting in smaller coupling factors. A
consequence of such smaller coupling factors is that filter 10
exhibits a narrower bandwidth. Resonators and coupling structures
appropriate for employment in filter 10 may be embodied in
different topologies. For example, resonators may be configured as
lumped elements for high frequency (HF) applications. Coaxial
cavities or transmission lines based on coaxial, microstrip, or
stripline lines can be used for low frequency RF applications.
Dielectric resonators or waveguides can be used for higher
frequency applications. The coupling mechanism between resonators
can be capacitive or inductive.
[0031] FIG. 2 shows another example of a tunable bandwidth filter
30 constructed in accordance with this invention using microstrip
technology. Filter 30 includes two edge coupled microstrip line
resonators 32, 34. An input microstrip line resonator 36 is
provided for delivering a signal to filter 30. An output microstrip
line resonator 38 is provided for receiving a signal from filter
30. In order to tune the bandwidth of filter 30, the coupling
factor between resonators, as well as, between input/output
transmission lines and the resonators should be changed. Tunable
varactors 40, 42 and 44 are provided for coupling resonators 32,
34, 36, 38. Varactors 40, 42, 44 are coupled between resonators 32,
34, 36, 38. Changing bias voltage to a respective varactor 40, 42,
44 changes the capacitance value for the respective varactor 40,
42, 44 which changes the coupling factor for the respective
varactor 40, 42, 44. By effecting changes in the coupling factors
of respective varactors 40, 42, 44, the bandwidth of filter 30 may
be altered. Both the access coupling and intercavity couplings are
capacitive in this exemplary embodiment illustrated in FIG. 2.
[0032] As illustrated by exemplary filters 10, 30 (FIGS. 1 and 2),
electrically tunable bandwidth filters use electronically tunable
varactors to tune intercavity coupling, thus varying the coupling
factor between the resonators, as well as, access coupling. The
varactor capacitance may be variously changed among respective
varactors by applying different bias voltages to different
varactors. In such manner the coupling factors of various varactors
may be varied, and bandwidth of the filter in which the varactors
are employed may be adjusted.
[0033] FIG. 3 is a top plan view of a varactor 50 that can be used
in the filters of this invention. FIG. 4 is a cross-sectional view
of the varactor of FIG. 3, taken along section 4-4 of FIG. 3. In
FIGS. 3 and 4, a varactor 50 includes a layer 52 of voltage tunable
dielectric material positioned on a surface 54 of a low loss, low
dielectric substrate 56. A pair of electrodes 58, 60 are positioned
on layer 52 and separated by a gap 62. An input line 64 is
connected with electrode 58 and an output line 66 is connected with
electrode 60. A variable DC voltage source 68 is connected between
electrodes 58, 60 to supply a control voltage to varactor 50. By
changing the control voltage provided by voltage source 58, the
capacitance of varactor 50 can be altered.
[0034] Filters configured according to the teachings of the present
invention (e.g., filter 10, FIG. 1; filter 30, FIG. 2; filter 50,
FIGS. 3 and 4) have low insertion loss, fast tuning speed, high
power-handling capability, high IP3 and low cost in the microwave
frequency range. Compared to the semiconductor diode varactors,
voltage-controlled tunable dielectric capacitors have higher Q
factors, higher power-handling and higher IP3. Voltage-controlled
tunable dielectric capacitors (e.g., varactors 20, 22, 24, 26, FIG.
1; varactors 40, 42, 44, FIG. 2; varactor 50, FIG. 3) have a
capacitance that varies approximately linearly with applied voltage
and can achieve a wider range of capacitance values than is
possible with semiconductor diode varactors.
[0035] Filters 10, 30, 50 described above can also serve as tunable
delay filters. Tunable delay filters can be used in various
devices, such as feed forward amplifiers. FIG. 5 is a schematic
representation of feed forward amplifier 70 including tunable delay
filters in accordance with this invention. A radio frequency (RF)
signal is input to an input port 72 and split by a signal splitter
74 into first and second parts. The first part on a line 76 goes to
a main amplifier 78 via a gain and phase adjustment device 80. The
output of main amplifier 78 on line 82 is a high level, distorted
carrier signal. A portion of this amplified and distorted carrier
signal is extracted using a directional coupler 84 and provided to
a carrier cancellation device 88 via an attenuator 86.
[0036] The second part of the RF signal received at signal splitter
74 is directed on a line 90 to carrier cancellation device 88 via a
delay device 92. Delay device 92 is configured to phase match
signals arriving at carrier cancellation device 88 from lines 76,
90. The signal arriving at carrier cancellation device 88 goes to a
main amplifier 78 via a gain and phase adjustment device 80.
[0037] The output of carrier cancellation device 88 is a low level
error or distortion signal. This signal, after passing through
another gain and phase adjustment device 94, is amplified by a low
power amplifier 96. An output signal from low power amplifier 96 is
provided to a subtractor device 98. A main distorted signal is
provided to subtractor 98 from directional coupler 84 via a delay
device 100. Subtractor 98 produces a difference signal at an output
102 representing the difference between signals provided to
subtractor 98 from delay device 100 and from low power amplifier
96. The difference signal appearing at output 102 the desired
non-distorted output carrier signal.
[0038] One or both of the delay devices 92, 100 in FIG. 5 can be a
tunable delay filter. By changing the bias voltage of varactor 42
in filter 30 (FIG. 2), for example, its capacitance value will
change which provides a change in its coupling factor. Similarly
the input/output access coupling for filter 30 can be varied by
tuning the corresponding varactors 40, 42. Changing the coupling
factors of filter 30 changes the bandwidth, which will result in
changing the group delay. Therefore, by tuning the coupling
varactors 40, 42 the group delay of filter 30 can be changed.
[0039] Resonators and coupling structures can be embodied in
different topologies. For example, resonators can be lumped
elements for HF applications; coaxial cavities or transmission
lines based on coaxial lines, microstrip lines, or stripline lines
can be used for low frequency RF applications; and dielectric
resonators or waveguides can be used for higher frequency
applications. Coupling structures can be capacitive or inductive.
The above described structures are only examples. Electronically
tunable varactors can be used to tune the coupling factors and
hence the bandwidth of any bandpass filter design to provide
variable group delay.
[0040] The invention also encompasses a method of delaying an
electrical signal, the method comprising the steps of: providing
first and second resonators, an input, a first tunable dielectric
varactor connecting the input to the first resonator, an output, a
second tunable dielectric varactor connecting the second resonator
to the output, and a third tunable dielectric varactor connecting
the first and second resonators; coupling the electrical signal to
the input; and extracting a delayed version of the electrical
signal at the output.
[0041] The tunable dielectric varactors in the preferred
embodiments of the present invention can include a low loss
(Ba,Sr)TiO.sub.3-based composite film. The typical Q factor of the
tunable dielectric capacitors is 200 to 500 at 2 GHz with
capacitance ratio (C.sub.max/C.sub.min) around 2. A wide range of
capacitance of the tunable dielectric capacitors is variable, say
0.1 pF to 10 pF. The tuning speed of the tunable dielectric
capacitor is less than 30 ns. The practical tuning speed is
determined by auxiliary bias circuits. The tunable dielectric
capacitor may be a packaged two-port component, in which tunable
dielectric material can be voltage-controlled. The tunable film may
preferably be deposited on a substrate, such as MgO, LaAlO.sub.3,
sapphire, Al.sub.2O.sub.3 and other dielectric substrates. An
applied voltage produces an electric field across the tunable
dielectric, which produces a change in the capacitance of the
tunable dielectric capacitor.
[0042] Tunable dielectric materials have been described in several
patents. Barium strontium titanate (BaTiO.sub.3--SrTiO.sub.3), also
referred to as BSTO, is used for its high dielectric constant
(200-6,000) and large change in dielectric constant with applied
voltage (25-75 percent with a field of 2 Volts/micron). Tunable
dielectric materials including barium strontium titanate are
disclosed in U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled
"Ceramic Ferroelectric Composite Material--BSTO--MgO"; U.S. Pat.
No. 5,635,434 by Sengupta, et al. entitled "Ceramic Ferroelectric
Composite Material--BSTO-Magnesium Based Compound"; U.S. Pat. No.
5,830,591 by Sengupta, et al. entitled "Multilayered Ferroelectric
Composite Waveguides"; U.S. Pat. No. 5,846,893 by Sengupta, et al.
entitled "Thin Film Ferroelectric Composites and Method of Making";
U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled "Method of
Making Thin Film Composites"; U.S. Pat. No. 5,693,429 by Sengupta,
et al. entitled "Electronically Graded Multilayer Ferroelectric
Composites"; U.S. Pat. No. 5,635,433 by Sengupta entitled "Ceramic
Ferroelectric Composite Material BSTO--ZnO"; U.S. Pat. No.
6,074,971 by Chiu et al. entitled "Ceramic Ferroelectric Composite
Materials with Enhanced Electronic Properties BSTO--Mg Based
Compound-Rare Earth Oxide". These patents are incorporated herein
by reference.
[0043] Barium strontium titanate of the formula
Ba.sub.xSr.sub.1-xTiO.sub.-3 is a preferred electronically tunable
dielectric material due to its favorable tuning characteristics,
low Curie temperatures and low microwave loss properties. In the
formula Ba.sub.xSr.sub.1-xTiO.sub.3, x can be any value from 0 to
1, preferably from about 0.15 to about 0.6. More preferably, x is
from 0.3 to 0.6.
[0044] Other electronically tunable dielectric materials may be
used partially or entirely in place of barium strontium titanate.
An example is Ba.sub.xCa.sub.1-xTiO.sub.3, where x is in a range
from about 0.2 to about 0.8, preferably from about 0.4 to about
0.6. Additional electronically tunable ferroelectrics include
Pb.sub.xZr.sub.1-xTiO.sub.3 (PZT) where x ranges from about 0.0 to
about 1.0, Pb.sub.xZr.sub.1-xSrTiO-.sub.3 where x ranges from about
0.05 to about 0.4, KTa.sub.xNb.sub.1-xO.sub.3 where x ranges from
about 0.0 to about 1.0, lead lanthanum zirconium titanate (PLZT),
PbTiO.sub.3, BaCaZrTiO.sub.3, NaNO.sub.3, KNbO.sub.3, LiNbO.sub.3,
LiTaO.sub.3, PbNb.sub.2O.sub.6, PbTa.sub.2O.sub.6, KSr(NbO.sub.3)
and NaBa.sub.2(NbO.sub.3).sub.5KH.sub.2-PO.sub.4, and mixtures and
compositions thereof. Also, these materials can be combined with
low loss dielectric materials, such as magnesium oxide (MgO),
aluminum oxide (Al.sub.2O.sub.3), and zirconium oxide (ZrO.sub.2),
and/or with additional doping elements, such as manganese (MN),
iron (Fe), and tungsten (W), or with other alkali earth metal
oxides (i.e. calcium oxide, etc.), transition metal oxides,
silicates, niobates, tantalates, aluminates, zirconnates, and
titanates to further reduce the dielectric loss.
[0045] In addition, the following U.S. patent applications,
assigned to the assignee of this application, disclose additional
examples of tunable dielectric materials: U.S. application Ser. No.
09/594,837 filed Jun. 15, 2000, entitled "Electronically Tunable
Ceramic Materials Including Tunable Dielectric and Metal Silicate
Phases"; U.S. application Ser. No. 09/768,690 filed Jan. 24, 2001,
entitled "Electronically Tunable, Low-Loss Ceramic Materials
Including a Tunable Dielectric Phase and Multiple Metal Oxide
Phases"; U.S. application Ser. No. 09/882,605 filed Jun. 15, 2001,
entitled "Electronically Tunable Dielectric Composite Thick Films
And Methods Of Making Same"; U.S. application Ser. No. 09/834,327
filed Apr. 13, 2001, entitled "Strain-Relieved Tunable Dielectric
Thin Films"; and U.S. provisional application Ser. No. 60/295,046
filed Jun. 1, 2001 entitled "Tunable Dielectric Compositions
Including Low Loss Glass Frits". These patent applications are
incorporated herein by reference.
[0046] The tunable dielectric materials can also be combined with
one or more non-tunable dielectric materials. The non-tunable
phase(s) may include MgO, MgAl.sub.2O.sub.4, MgTiO.sub.3,
Mg.sub.2SiO.sub.4, CaSiO.sub.3, MgSrZrTiO.sub.6, CaTiO.sub.3,
Al.sub.2O.sub.3, SiO.sub.2 and/or other metal silicates such as
BaSiO.sub.3 and SrSiO.sub.3. The non-tunable dielectric phases may
be any combination of the above, e.g., MgO combined with
MgTiO.sub.3, MgO combined with MgSrZrTiO.sub.6, MgO combined with
Mg.sub.2SiO.sub.4, MgO combined with Mg.sub.2SiO.sub.4,
Mg.sub.2SiO.sub.4 combined with CaTiO.sub.3 and the like.
[0047] Additional minor additives in amounts of from about 0.1 to
about 5 weight percent can be added to the composites to
additionally improve the electronic properties of the films. These
minor additives include oxides such as zirconnates, tannates, rare
earths, niobates and tantalates. For example, the minor additives
may include CaZrO.sub.3, BaZrO.sub.3, SrZrO.sub.3, BaSnO.sub.3,
CaSnO.sub.3, MgSnO.sub.3, Bi.sub.2O.sub.3/2SnO.sub.2,
Nd.sub.2O.sub.3, Pr.sub.7O.sub.11, Yb.sub.2O.sub.3,
Ho.sub.2O.sub.3, La.sub.2O.sub.3, MgNb.sub.2O.sub.6,
SrNb.sub.2O.sub.6, BaNb.sub.2O.sub.6, MgTa.sub.2O.sub.6,
BaTa.sub.2O.sub.6 and Ta.sub.2O.sub.3.
[0048] Thick films of tunable dielectric composites can comprise
Ba.sub.1-xSr.sub.xTiO.sub.3, where x is from 0.3 to 0.7 in
combination with at least one non-tunable dielectric phase selected
from MgO, MgTiO.sub.3, MgZrO.sub.3, MgSrZrTiO.sub.6,
Mg.sub.2SiO.sub.4, CaSiO.sub.3, MgAl.sub.2O.sub.4, CaTiO.sub.3,
Al.sub.2O.sub.3, SiO.sub.2, BaSiO.sub.3 and SrSiO.sub.3. These
compositions can be BSTO and one of these components or two or more
of these components in quantities from 0.25 weight percent to 80
weight percent with BSTO weight ratios of 99.75 weight percent to
20 weight percent.
[0049] The electronically tunable materials can also include at
least one metal silicate phase. The metal silicates may include
metals from Group 2A of the Periodic Table, i.e., Be, Mg, Ca, Sr,
Ba and Ra, preferably Mg, Ca, Sr and Ba. Preferred metal silicates
include Mg.sub.2SiO.sub.4, CaSiO.sub.3, BaSiO.sub.3 and
SrSiO.sub.3. In addition to Group 2A metals, the present metal
silicates may include metals from Group 1A, i.e., Li, Na, K, Rb, Cs
and Fr, preferably Li, Na and K. For example, such metal silicates
may include sodium silicates such as Na.sub.2SiO.sub.3 and
NaSiO.sub.3-5H.sub.2O, and lithium-containing silicates such as
LiAlSiO.sub.4, Li.sub.2SiO.sub.3 and Li.sub.4SiO.sub.4. Metals from
Groups 3A, 4A and some transition metals of the Periodic Table may
also be suitable constituents of the metal silicate phase.
[0050] Additional metal silicates may include
Al.sub.2Si.sub.2O.sub.7, ZrSiO.sub.4, KalSi.sub.3O.sub.8,
NaAlSi.sub.3O.sub.8, CaAl.sub.2Si.sub.2O.sub.8,
CaMgSi.sub.2O.sub.6, BaTiSi.sub.3O.sub.9 and Zn.sub.2SiO.sub.4. The
above tunable materials can be tuned at room temperature by
controlling an electric field that is applied across the
materials.
[0051] In addition to the electronically tunable dielectric phase,
the electronically tunable materials can include at least two
additional metal oxide phases. The additional metal oxides may
include metals from Group 2A of the Periodic Table, i.e., Mg, Ca,
Sr, Ba, Be and Ra, preferably Mg, Ca, Sr and Ba. The additional
metal oxides may also include metals from Group 1A, i.e., Li, Na,
K, Rb, Cs and Fr, preferably Li, Na and K. Metals from other Groups
of the Periodic Table may also be suitable constituents of the
metal oxide phases. For example, refractory metals such as Ti, V,
Cr, Mn, Zr, Nb, Mo, Hf, Ta and W may be used. Furthermore, metals
such as Al, Si, Sn, Pb and Bi may be used. In addition, the metal
oxide phases may comprise rare earth metals such as Sc, Y, La, Ce,
Pr, Nd and the like.
[0052] The additional metal oxides may include, for example,
zirconnates, silicates, titanates, aluminates, stannates, niobates,
tantalates and rare earth oxides.
[0053] Preferred additional metal oxides include Mg.sub.2SiO.sub.4,
MgO, CaTiO.sub.3, MgZrSrTiO.sub.6, MgTiO.sub.3, MgAl.sub.2O.sub.4,
WO.sub.3, SnTiO.sub.4, ZrTiO.sub.4, CaSiO.sub.3, CaSnO.sub.3,
CaWO.sub.4, CaZrO.sub.3, MgTa.sub.2O.sub.6, MgZrO.sub.3, MnO.sub.2,
PbO, Bi.sub.2O.sub.3 and La.sub.2O.sub.3. Particularly preferred
additional metal oxides include Mg.sub.2SiO.sub.4, MgO,
CaTiO.sub.3, MgZrSrTiO.sub.6, MgTiO.sub.3, MgAl.sub.2O.sub.4,
MgTa.sub.2O.sub.6 and MgZrO.sub.3.
[0054] The additional metal oxide phases are typically present in
total amounts of from about 1 to about 80 weight percent of the
material, preferably from about 3 to about 65 weight percent, and
more preferably from about 5 to about 60 weight percent. In one
preferred embodiment, the additional metal oxides comprise from
about 10 to about 50 total weight percent of the material. The
individual amount of each additional metal oxide may be adjusted to
provide the desired properties. Where two additional metal oxides
are used, their weight ratios may vary, for example, from about
1:100 to about 100:1, typically from about 1:10 to about 10:1 or
from about 1:5 to about 5:1. Although metal oxides in total amounts
of from 1 to 80 weight percent are typically used, smaller additive
amounts of from 0.01 to 1 weight percent may be used for some
applications.
[0055] In one embodiment, the additional metal oxide phases may
include at least two Mg-containing compounds. In addition to the
multiple Mg-containing compounds, the material may optionally
include Mg-free compounds, for example, oxides of metals selected
from Si, Ca, Zr, Ti, Al and/or rare earths. In another embodiment,
the additional metal oxide phases may include a single
Mg-containing compound and at least one Mg-free compound, for
example, oxides of metals selected from Si, Ca, Zr, Ti, Al and/or
rare earths. The high Q tunable dielectric capacitor utilizes low
loss tunable substrates or films.
[0056] To construct a tunable device, the tunable dielectric
material can be deposited onto a low loss substrate. In some
instances, such as where thin film devices are used, a buffer layer
of tunable material, having the same composition as a main tunable
layer, or having a different composition can be inserted between
the substrate and the main tunable layer. The low loss dielectric
substrate can include magnesium oxide (MgO), aluminum oxide
(Al.sub.2O.sub.3), and lanthium oxide (LaAl.sub.2O.sub.3).
[0057] When the bias voltage or bias field is changed, the
dielectric constant of the voltage tunable dielectric material
(di-elect cons..sub.r) will change accordingly, which will result
in a tunable varactor. Compared to semiconductor varactor based
tunable filters, the tunable dielectric capacitor based tunable
filters of this invention have the merits of lower loss, higher
power-handling, and higher IP3, especially at higher frequencies
(>10 GHz). It is observed that between 50 and 300 volts a nearly
linear relation exists between Cp and applied Voltage.
[0058] In microwave applications the linear behavior of a
dielectric varactor is very much appreciated, since it will assure
very low Inter-Modulation Distortion and consequently a high IP3
(Third-order Intercept Point). Typical IP3 values for diode
varactors are in the range 5 to 35 dBm, while that of a dielectric
varactor is greater than 50 dBm. This will result in a much higher
RF power handling capability for a dielectric varactor.
[0059] Another advantage of dielectric varactors compared to diode
varactors is the power consumption. The dissipation factor for a
typical diode varactor is in the order of several hundred
milliwatts, while that of the dielectric varactor is about 0.1
mW.
[0060] Diode varactors show high Q only at low microwave
frequencies so their application is limited to low frequencies,
while dielectric varactors show good Q factors up to millimeter
wave region and beyond (up to 60 GHz).
[0061] Tunable dielectric varactors can also achieve a wider range
of capacitance (from 0.1 pF all the way to several .mu.F), than is
possible with diode varactors. In addition, the cost of dielectric
varactors is less than diode varactors, because they can be made
more cheaply.
[0062] High frequency, radio frequency, and microwave bandpass
filters of this invention include a number of resonators and some
coupling structures. The resonators can be lumped elements, any
type of transmission lines, dielectric resonators, waveguides, or
other resonating structures. The coupling mechanism between the
adjacent resonators as well as the access transmission line and
first and last resonators can be tuned electronically by using
tunable dielectric varactors. Tuning the coupling factors of the
bandpass filter results in tunable bandwidth filter.
[0063] Electronically tunable dielectric varactors may be used to
make tunable delay filters. The invention also relates to compact,
high performance, low loss, and low cost tunable delay filters.
These compact tunable delay filters are increasingly being used in
feed-forward or pre-distortion technologies used in high power
amplifiers in wireless communication base stations and other
communication systems. The high Q varactor using low loss tunable
dielectric material films leads to high performance tunable delay
filters with significant advantages over fixed delay filters and
coaxial cable delay lines.
[0064] The electronically tunable delay filters of this invention
use electronically tunable varactors to tune the group delay of the
filter. When the varactor capacitance is changed by applying
different bias voltages, the coupling factors between the filter
resonators are varied, which result in a change in filter group
delay value. Electrically tunable delay filters based on dielectric
varactors have important advantages such as high Q, small size,
lightweight, low power consumption, simple control circuits, and
fast tuning capability. Compared with semiconductor diode
varactors, dielectric varactors have the merits of lower loss,
higher power-handling, higher IP3, faster tuning speed, and lower
cost.
[0065] The tunable delay filters include a number of resonators and
some coupling structures. The resonators can be lumped element, any
type of transmission line, dielectric resonator, waveguide, or
another resonator structure. The coupling mechanism between the
adjacent resonators as well as the access transmission line and
first and last resonators can be tuned electronically by using
voltage tunable dielectric varactors. Tuning the coupling factors
of the bandpass filter will result in tunable delay filter. Some
filter examples are provided, but the patent is not limited to
those structures.
[0066] This invention provides an effective way of designing a
tunable delay filter. When used in a feed forward amplifier the
filters provide an easy way of inducing delay as well as tuning
delay to obtain distortion free output signals from power
amplifiers. Improved tuning delay can result in better modulated
signals. Tunable delay filters can reduce the system cost and
significantly improve the quality of radio link.
[0067] This invention provides electrically tunable bandwidth and
tunable delay filters having high Q, small size, light weight, low
power consumption, simple control circuits, and fast tuning
capability.
[0068] FIG. 6 is a flow diagram illustrating the method of the
present invention. In FIG. 6, a method 200 for delaying an
electrical signal begins at a START locus 202. Method 200 continues
with providing a plurality of resonator units coupled between an
input locus and an output locus, as indicated by a block 204.
[0069] Method 200 continues with providing a plurality of tunable
dielectric varactor units, as indicated by a block 206. Respective
individual varactor units of the plurality of varactor units are
coupled between respective pairs of the plurality of resonator
units, coupled between the plurality of resonator units and the
input locus, and coupled between the plurality of resonator units
and the output locus. Each respective individual varactor unit
includes a substrate, a layer of voltage tunable dielectric
material established in a first land on the substrate, a first
electrode structure for receiving an electrical signal established
in a second land on the first land, and a second electrode
structure for receiving an electrical signal established in a third
land on the first land. The first land and the second land are
separated by a gap.
[0070] Method 200 continues with applying the electrical signal to
the input locus, as indicated by a block 208. Method 200 continues
with applying a respective tuning voltage to the first electrode
structure and the second electrode structure of each respective
varactor unit, as indicated by a block 210. Each respective
varactor unit exhibits a respective capacitance. The respective
capacitance varies in response to the respective tuning
voltage.
[0071] Method 200 continues with receiving an output signal at the
output locus, as indicated by a block 212. The output signal is
delayed with respect to the electrical signal. Method 200 then
terminates, as indicated by an END locus 214.
[0072] Another application where a tunable delay line may be used
in an embodiment of the present invention is in a feed forward
amplifier with multiple cancellation loops capable of reducing
intermodulation distortion and receives band noise. The use of
Feedforward technique to reduce intermodulation distortion, caused
by the power amplifier in the transmit (Tx) path is well known. The
above articulated tunable delay line used in the feed forward
cancellation loop, based on BST tunable dielectric material, has
been shown to provide significant reduction of intermodulation
signals. In an embodiment of the present invention, by adding at
least one additional loop, the noise signal in the Rx band may be
reduced which helps relax the rejection requirement of the Tx
filter in the Duplexer and decreases the insertion loss, hence
increase the output power.
[0073] When amplifying the Tx band signal, Rx band noise signals
are also amplified and transferred to the duplexer 1280 of FIG. 12.
These signals may enter the receiver without attenuation and will
decrease signal to noise ratio (SNR) of the receiver. This could be
avoided by increasing the isolation between Tx and Rx in the
Duplexer, but it would require front end Tx filter with more
rejection, with associated higher insertion loss. In an embodiment
of the present invention, an alternative approach is to use at
least one additional loop and in one embodiment a second loop in
the feedforward amplifier to reduce this noise.
[0074] Turning now to the figures, FIGS. 7-12 are shown generally
at 700, 800, 900, 1000, 1100, 1200. FIG. 7 illustrates a signal
spectrum at the input which includes a transmit signal and receive
noise of one embodiment of the present invention with the input
signal in the transmit path which contains Tx signal, and some
noise in the Rx band with f1 710 and f2 720 being two tones of
noise in Rx band and f3 730 and f4 740 are two tones in Tx band.
FIG. 8 illustrates a signal spectrum at point "a" of FIG. 12
including a transmit signal 840 and 850 and receive noise 810 and
820 and intermodulation signals 830 and 860 one embodiment of the
present invention.
[0075] FIG. 9 illustrates the signal spectrum at point "b" of FIG.
12 and intermodulation signals 910 and 920 of one embodiment of the
present invention. FIG. 10 illustrates the Signal spectrum at point
"c" of FIG. 12 with Transmit signal 1030 and 1040 and Receive noise
1010 and 1020 amplified of one embodiment of the present invention.
FIG. 11 illustrates the signal spectrum at point "d" of FIG. 12
with receive noise 1110 and 1120 of one embodiment of the present
invention.
[0076] Turning now to FIG. 12 is an illustration of a feed forward
power amplifier capable of reducing intermodulation distortion and
receive noise of one embodiment of the present invention. At input
1201 the input signal in the transmit path which contains Tx
signal, and some noise in the Rx band (illustrated at 1205). This
signal, after some amplitude 1245 and phase 1250 adjustment, will
reach the main power amplifier, PA 1255. The PA 1255 will amplify
the Tx signal, the Rx noise, and will generate some intermodulation
signals, as shown by the spectrum at point a 1211, with signal
vectors shown at 1210.
[0077] A portion of signal "a" 1211 is coupled off and then divided
in two halves by Wilkinson divider 1275, although the present
invention is not limited to any particular divider. One half will
go to the combiner 1270 after some amplitude 1260 adjustments. At
the input 1201, a portion of the input signal (signal vector shown
at 1225) will be coupled off and after passing through the tunabale
delay line 1265 will be subtracted from the signal coming from
point a 1211. The output of the combiner 1270 will therefore
contain only the intermodulation signal. This is achieved when the
two signals reaching the combiner 1270 have exactly the same
amplitude, and are out of phase. The presence of tunable delay line
1265 is necessary to achieve wide band cancellation. This signal,
after some amplitude 1203 and phase 1285 adjustments will be
amplified by an error amplifier, Amp 1290, shown at point b 1219.
Intermodulation and f1 and f2 signal vectors 1230 and 1235 and
shown at point b 1219.
[0078] The signal at point "b" 1219 will then be coupled, or
subtracted from signal "a" 1211 to give signal "c" 1221 without
intermodulation distortion. Signal vectors for point "c" is shown
at 1215 and 1220. The cancellation is achieved, when the amplitude
of this signal is exactly equal to the amplitude of intermodulation
signal at point "a" 1211 with 180 phase shift. It is observed that
the noise in the receive band, f1 and f2, are still present at
point "c" 1221 as shown at 1215. The purpose of the second loop is
to eliminate this noise, as described below.
[0079] The other half of signal "a" 1211 from Divider 1275 will go
through a bandpass filter 1295 at the frequency of Rx. This filter
1295 will reject Tx signal and intermodulation signals.
Alternatively, a notch filter could be used to reject the Tx
spectrum and it is understood that the present invention is not
limited to any particular types of filters. This signal, after
going through a tunable delay line 1297, phase shifter P 1299, and
attenuator A 1202, will be amplified using an error amplifier Amp
1204. Again, the role of tunable delay line is crucial in achieving
wide band cancellation and to compensate for any temperature drift
in other components of the loop. The signal at point "d" 1217 only
contains the Rx noise signal f1 and f2 1219.
[0080] Similar to the first cancellation loop, the signal at point
"d" 1217 will be subtracted from the signal at pint "c" 1221
resulting in the output transmit signal 1223 containing only the Tx
tones 1220.
[0081] It is to be understood that, while the detailed drawings and
specific examples given describe preferred embodiments of the
invention, they are for the purpose of illustration only, that the
apparatus and method of the invention are not limited to the
precise details and conditions disclosed and that various changes
may be made therein without departing from the spirit of the
invention which is defined by the following claims:
* * * * *